Relative to resting lymphocytes, both activated lymphocytes and lymphoma cells exhibit a distinct shift is cell metabolism from oxidative phosphorylation, which generates mostly ATP for energy, to aerobic glycolysis, which generates bioprecursors such as amino acids, lipids, and nucleic acids required to fuel cell division. An understanding of the factors that control this switch (termed the Warburg Effect) is highly significant because it could lead to innovative strategies to selectively kill activated lymphocyte in autoimmune disease and lymphoma cells in cancer. Our long-term goals are to understand the biological roles and mechanism of action of a novel family of metabolic regulating proteins called Folliculin Interacting Proteins (consisting of Fnip1 and Fnip2) in lymphocyte development, activation, metabolism, autoimmunity, and lymphomagenesis. We hypothesize that Fnip1 and Fnip2 are critical for maintaining metabolic balance in response to energy stress, such as during lymphocyte activation, nutrient deprivation, and oncogene activation. We previously utilized an ENU chemical mutagenesis strategy in mice to identify an innovative new strain that lacks B lymphocytes due to a deletion in the Fnip1 gene. Fnip1-null mice have a complete block in B cell development at the pre-B cell stage, and fail to mature and activate in response to enforced IgM expression suggesting an important role for Fnip1 in mature B cells as well. Fnip1 deficient pre-B cells are exquisitely sensitive to cell death in response to antigen receptor stimulation, nutrient deprivation, and are resistant to transformation by the Myc oncogene. Surprisingly, T cell development and function is normal in Fnip1 null mice. Although the functions of Fnip1 and Fnip2 are not known, both molecules interact with Folliculin and the master metabolic regulator AMP kinase (AMPK). In response to low energy, AMPK is normally activated to turn on metabolic pathways that generate energy while shutting off energy consuming pathways regulated by mammalian target of rapamyin (mTOR). The overall goal of this proposal is to define the importance of Fnip1 and Fnip2 in lymphocyte development and autoimmunity. Our Specific Aims are: (1) To define the roles of Fnip1 in mature B cell activation, survival, and metabolism. We will inhibit Fnip1 specifically in mature B cells and will determine the affects of Fnip1 loss on peripheral B cell development, survival, and sensitivity to autoimmune disease; and (2) To determine the importance of Fnip2 in B and T lymphocyte development. We will generate Fnip2 deficient mice and will determine the whether Fnip2 is essential for B and T cell development. These studies are highly innovative because they define the importance of a new family of metabolic proteins in lymphocyte development and activation, address a critical need to identify metabolic regulators as potential targets in autoimmune disease and cancer, and generate essential Fnip-deficient mouse models to test the efficacy of inhibiting Fnip1 or Fnip2 in immune-mediated diseases, cancer, obesity, and other metabolic diseases.